The present invention relates to a rotor assembly for an airplane gas turbine engine. More particularly, it relates to blade platforms for the fan portion of such an engine, but it is equally applicable to platforms for mounting blades in other rotary assemblies, e.g. in the compressor.
In known manner, the fan of a gas turbine engine comprises a disk having angularly spaced-apart blades received so as to be pivotable to a small extent. Each blade is connected to the two blades adjacent thereto via force transmitter members (also referred to as platforms) which serve under normal circumstances to limit pivoting of the blades. These platforms also serve to protect the disk and the blades of the fan, which parts are expensive.
At present, there are two types of blade platforms for gas turbine engine fans and they are made using the following technologies:
platforms that are directly integrated with the blades for straight fastenings; and
platforms fitted between the blades.
By way of example, for platforms fitted between the blades, one known system consists in holding the platform, e.g. made of aluminum, by means of pegs which are fixed on flanges of the fan disk and to a cheek plate provided at the front of the disk. The assembly is sealed by lateral gaskets of rubber which are pressed and deformed against the blades by the centrifugal force that results from the fan disk rotating.
That platform-holding system presents a major problem associated with the platform balancing to be performed by the pegs, and with controlling displacements between the pegs and the platform.
Furthermore, the problems encountered in operation are numerous, and in particular the following:
the sealing gaskets lift off;
the bushings of the holding pegs move in translation, in spite of being clamped when the platform is assembled;
the pegs become loose relative to the flanges; and
there is a risk of corrosion.
In addition, problems of wear are observed on the bearing surfaces of the blades and of the disk of the fan. In order to resolve those problems, and more particularly the problem relating to bearing surface wear, it is also known to re-machine the recess of the disk in which the blade root is mounted, and to insert a piece of metal that acts as shim (also referred to as xe2x80x9ctinselxe2x80x9d).
Nevertheless, in spite of the presence of the shim, it is still found that the deposit of varnish type antiwear material lifts off from the bearing surfaces of the blades and of the fan disk. Furthermore, reboring is an operation that is difficult and time consuming.
The present invention seeks to propose a platform fitted to blades and a rotary assembly using such a platform while avoiding the above drawbacks.
To this end, the invention provides a rotary assembly comprising a disk having recesses at its periphery, a plurality of blades carried by the disk, each blade having a blade root engaged in a corresponding recess of the disk, and a plurality of fitted platforms each mounted on the disk between two adjacent blades, wherein each platform is a piece of sheet metal of substantially omega section having two flanks interconnected by a web and shaped so as to press against the side walls of the bottom portions of two adjacent blades, with the end portions of the flanks presenting respective setbacks which fit closely to the outlines of one side of a blade root and of the adjacent side of the wall of a recess in which the blade root is received.
This particular platform shape makes it possible both to protect the blades and the disks, and also to provide sealing for the assembly.